Guy Boos KIN 470 12 11 15 Lab 6 INTRODUCTION Muscular strength and the magnitude of the force it produces is dependent on how large the cross section of the muscle is About 2 3 of muscular strength comes from the size of the muscle which also correlates to how large the cross section is The larger the cross section the more sarcomeres which are the contracting unit of a muscle fiber With a larger amount of sarcomeres present the more force that can be produced It is important to note that when comparing the muscular force production of males to females males produce more force due to the presence of testosterone which is the hormone that promotes muscle growth Muscular force is created when muscles contract Contractions occur when actin and myosin bind and creating tension within the muscle Actin and myosin are proteins that are found within myofibrils which are rod shaped muscle fibers The myofibril contains two types of fibers thick which are composed of myosin and thin which are composed of actin The presence of calcium is what creates these contractions and until calcium is present contractions will continue to occur When muscles are contracted for a prolonged period of time or repeated contractions they begin to fatigue Fatigue occurs when a build up of pH or hydrogen ions and inorganic phosphate accumulate in the muscle The increase in pH is detrimental to producing contractions because the increase in Hydrogen ions creates competition at the binding site of troponin with calcium This competition creates a decrease in contraction because if calcium doesn t bind with troponin then cross bridges do not form Inorganic phosphate is formed when adenosine diphosphate is bonded with phosphate The build up of inorganic phosphate moved from the myofibril into the sarcoplasmic reticulum which the precipitates and creates salt which inhibits the abilities of the muscle to contract Their endurance during these contractions is dependent on the type of muscle fiber being used Type I muscle fibers produce less force than Type II muscle fibers but are more resistant to fatigue This is due to characteristics of being low long lasting force production that run off of aerobic energy systems Type II muscle fibers are the opposite of type I muscles fibers in that they are fast and produce high amounts of force but quickly fatigue due to their dependency on anaerobic energy systems such as glycolysis Two types of fatigues can occur peripheral and central Peripheral fatigue occurs when factors that are involved with creating action potentials and chemical transmitted are inhibited Examples of this type of fatigue are the inhibition of calcium release or the depletion of ATP levels throughout exercise Central fatigue occurs when factors within the muscle inhibit or decrease muscle interaction A primary example of central fatigue is the decrease in motor discharge units which occur during prolonged submaximal contractions Another important factor in muscular strength and endurance is rate coding and rate recruitment The rate at which both are used depends on the amount of force that is needed The amount of fibers recruited to produce force is smaller for smaller contractions and larger for larger contractions Recruitment follows the all or none principle which states that when a motor unit is innervated by an action potential the entirety of the unit is used and not just part of it The size of the action potential is what determines how many motor units will be innervated where larger action potentials create larger motor unit recruitments and smaller action potentials lead to motor units rejecting the innervation When fatigue occurs during a submaxiaml and prolonged contraction more and more motor units are recruited to keep up with the demand the body is asking of it This is done by recruiting larger motor units such as type II muscle fibers Rate coding is the the rate at which motor units are recruited Since motor units are initiated through action potentials the number of action potentials that travel down motor units per second is rate of coding When a muscle fatigues the rate at which motor units are recruited begins to slow and EMG activity during prolonged submaximal shows this by having smaller ranges between the peak and valleys of the electrical signals METHODS 1 To begin this lab the class was broken up into groups of three to five people to test determine maximal voluntary contraction or MVC Each group was given a computer with Biopac already uploaded onto the screen From Biopac a program that would be measuring the forces produced called the Muscle Endurance lab was to be used to measure the forces produced during the test Each participant would take turns holding the hand grip dynamometer with elbows resting on the tables to that their forearm was in an upright position After the operator of the computer clicked start the subject would squeeze as hard as possible for about 3 to 4 seconds which was kept track of using a stopwatch The operator would then hit stop to end the test This was repeated for all subjects in all groups After the MVC test was complete each subject would measure their forearm circumference that was used in conducting the MVC using a measuring tape in centimeters Peak force was then calculated through the tools available within the Biopac program The next procedure in this lab was determining the fatigue and recovery of the participants with the lowest force production This was done with the same set up as the MVC but the amount of contractions and the duration of contractions was changed Each subject would perform twelve 10 second contraction cycles The pattern of this test followed a 7 second contraction phase followed by a 3 second rest phase After the twelve cycles were completed a new bout of contractions immediately followed The pattern of this new contraction cycle consisted of 3 4 second contractions immediately following the twelfth contraction 30 seconds after 60 seconds after 120 seconds after and finally 240 seconds after During the final test of this lab the endurance of the strongest members in each group was to be tested This was done by by picking three males and three females who had the highest force production determined by the MVC EMG stick pads were connected to the distal region of the radius the proximal region of the ulna and the back of the elbow on the dominant arm of the subject Given the MVC in the first test a calculation of 5 and 30